A negative impedance converter (NIC) is an active circuit device by means of which a passive arbitrary impedance may be transformed into its algebraic negative. For intance, a capacitor converted to the appropriate port of a NIC causes its other port to appear as a negative capacitor. This, of course, at certain frequencies determined by the bandwidth of the active components and other circuit parameters. Such devices are well known in the art.
The improvement of the present invention does not directly alter the operation of the otherwise known NIC circuit itself, although, of course, interaction therewith is unavoidable. By using an additional active device, an operational amplifier, the signal handling capability of the NIC is enhanced; the improved NIC circuit can handle a signal with greater amplitude.
Thus, according to the present invention there is provided an improved negative impedance converter comprising a conventional negative impedance converter having a negative impedance port and a positive impedance port, a differential operational amplifier having an inverting input and a non-inverting input and an output, said inverting input receiving one side of said negative impedance port, said non-inverting input receiving a reference voltage, and said output forming, with the other side of said negative impedance port, the output of said improved negative impedance converter.
In a preferred aspect of the present invention, said differential operational amplifier has its output and its inverting input interconnected with circuit means to provide a gain factor of minus one.
Such an improved negative impedance converter is utilized in the invention subject of copending application Ser. No. 824,659 filed in the name of Nachum Lichtenstein and having the assignee of the present application in common.